1. Field of the Invention
The present invention relates to a control system for a vehicular automatic transmission.
2. Related Art
Vehicular automatic transmissions are conventionally equipped with a shift map which is set beforehand with shift characteristics, so that a shift control may be effected by matching the running status of the vehicle with the shift map. The terminology "vehicular running status," as used herein has reference to a vehicle operating parameter or parameters such as vehicle speed or throttle opening.
Since, however, the control pattern in the shift control is set with reference to an ordinary run, an optimum gear stage is not always set when the vehicle encounters extraordinary road circumstances such as an incline which requires a driving force different from that required for level roads.
Japanese Patent Published No. 58141/1994 discloses a shift control system which monitors the actual detected road circumstances to improve the running safety and the driving comfort by utilizing a navigation system with the shift control so that the control pattern is changed on the basis of the road information obtained from the navigation system in addition to information regarding the running status of the vehicle.
Demands in recent years for lower power consumption to abate environmental pollution also dictate improvement in the aforementioned prior art shift control system which is based upon the running status of the vehicle, set with reference to "normal" running. Such prior art systems cannot provide optimum mileage because the fuel consumption rate changes with change in the required driving force, deriving from changes in the road circumstances.
Japanese application Laid-Open ("Kokai") No. 95721/1981 discloses a shift control system which improves the mileage by calculating the instantaneous driving force required of the vehicle so that a gear stage optimizing the mileage may be set by comparing the driving force with a mileage map.
While the system disclosed by Japanese Patent publication No. 58141/1994 effects shift control by matching the road circumstances, it does not satisfy the demand for increased fuel economy because the shift control does not take mileage into consideration.
On the other hand, Kokai No. 95721/1981 can effect shift control in such a way as to improve the mileage but cannot always provide satisfactory running safety or driving comfort because the shift control does not take into consideration the road circumstances actually encountered by the vehicle.